The major change is that Plack,
a toolkit for using the PSGI specification,
now replaces most of the subclasses of Catalyst::Engine.
If you are using one of the standard subclasses of Catalyst::Engine this should be a straightforward upgrade for you.
It was a design goal for this release to preserve as much backwards compatibility as possible.
However,
since Plack is different from Catalyst::Engine,
it is possible that differences exist for edge cases.
Therefore,
we recommend that care be taken with this upgrade and that testing should be greater than would be the case with a minor point update.
Please inform the Catalyst developers of any problems so that we can fix them and incorporate tests.

It is highly recommended that you become familiar with the Plack ecosystem and documentation.
Being able to take advantage of Plack development and middleware is a major bonus to this upgrade.
Documentation about how to take advantage of Plack::Middleware by writing your own .psgi file is contained in Catalyst::PSGI.

Catalyst::Engine::Apache2::MP19,
however,
is no longer supported,
as Plack does not support mod_perl version 1.99.
This is unlikely to be a problem for anyone,
as 1.99 was a brief beta-test release for mod_perl 2,
and all users of mod_perl 1.99 are encouraged to upgrade to a supported release of Apache 2 and mod_perl 2.

The default development server that comes with the Catalyst distribution should continue to work as expected with no changes as long as your myapp_server script is upgraded to use Catalyst::Script::HTTP.

Applications that were using Catalyst::Engine::PSGI previously should entirely continue to work in this release with no changes.

However, if you have an app.psgi script, then you no longer need to specify the PSGI engine. Instead, the Catalyst application class now has a new method psgi_app which returns a PSGI compatible coderef which you can wrap in the middleware of your choice.

Catalyst will use the .psgi for your application if it is located in the home directory of the application.

For example, if you were using Catalyst::Engine::PSGI in the past, you will have written (or generated) a script/myapp.psgi file similar to this one:

my $app = sub { MyCatalystApp->psgi_app(@_) };
# If you make ^^ this mistake, your app won't work, and will confuse the hell out of you!

You can now move script/myapp.psgi to myapp.psgi, and the built-in Catalyst scripts and your test suite will start using your .psgi file.

NOTE: If you rename your .psgi file without these modifications, then any tests run via Catalyst::Test will not be compatible with the new release, and will result in the development server starting, rather than the expected test running.

NOTE: If you are directly accessing $c->req->env to get the PSGI environment then this accessor is moved to $c->engine->env, you will need to update your code.

The following engines DO NOT work as of Catalyst version 5.9. The core team will be happy to work with the developers and/or users of these engines to help them port to the new Plack/Engine system, but for now, applications which are currently using these engines WILL NOT run without modification to the engine code.

However, a lot of refactoring work has taken place, and several changes have been made which could cause incompatibilities. If your application or plugin is using deprecated code, or relying on side effects, then you could have issues upgrading to this release.

Most issues found with existing components have been easy to solve. This document provides a complete description of behavior changes which may cause compatibility issues, and of new Catalyst warnings which might be unclear.

If you think you have found an upgrade-related issue which is not covered in this document, please email the Catalyst list to discuss the problem.

Applications must be in their own file, and loaded at compile time. This issue generally only affects the tests of CPAN distributions. Your application will fail if you try to define an application inline in a block, and use plugins which supply a new method, then use that application latter in tests within the same file.

This is due to the fact that Catalyst is inlining a new method on your application class allowing it to be compatible with Moose. The method used to do this changed in 5.80004 to avoid the possibility of reporting an 'Unknown Error' if your application failed to compile.

Catalyst 5.80 uses the Algorithm::C3 method dispatch order. This is built into Perl 5.10, and comes via Class::C3 for Perl 5.8. This replaces NEXT with Class::C3::Adopt::NEXT, forcing all components to resolve methods using C3, rather than the unpredictable dispatch order of NEXT.

This issue manifests itself by your application failing to start due to an error message about having a non-linear @ISA.

The Catalyst plugin most often causing this is Catalyst::Plugin::Session::Store::FastMmap - if you are using this plugin and see issues, then please upgrade your plugins, as it has been fixed. Note that Makefile.PL in the distribution will warn about known incompatible components.

This issue can, however, be found in your own application - the only solution is to go through each base class of the class the error was reported against, until you identify the ones in conflict, and resolve them.

To be able to generate a linear @ISA, the list of superclasses for each class must be resolvable using the C3 algorithm. Unfortunately, when superclasses are being used as mixins (to add functionality used in your class), and with multiple inheritance, it is easy to get this wrong.

Most common is the case of:

package Component1; # Note, this is the common case
use base qw/Class::Accessor::Fast Class::Data::Inheritable/;
package Component2; # Accidentally saying it this way causes a failure
use base qw/Class::Data::Inheritable Class::Accessor::Fast/;
package GoesBang;
use base qw/Component1 Component2/;

to use the constructor provided by Moose, while working (if you do some hacks with the BUILDARGS method), will not work with Catalyst 5.80 as Catalyst::Component inherits from Moose::Object, and so @ISA fails to linearize.

The correct way to use Moose in a component in a both forward and backwards compatible way is:

Note that the extends declaration needs to occur in a begin block for attributes to operate correctly.

This way you do not inherit directly from Moose::Object yourself. Having components which do not inherit their constructor from Catalyst::Component is unsupported, and has never been recommended, therefore you're on your own if you're using this technique. You'll need to detect the version of Catalyst your application is running, and deal with it appropriately.

You also don't get the Moose::Object constructor, and therefore attribute initialization will not work as normally expected. If you want to use Moose attributes, then they need to be made lazy to correctly initialize.

Note that this only applies if your component needs to maintain component backwards compatibility for Catalyst versions before 5.71001 - in 5.71001 attributes work as expected, and the BUILD method is called normally (although BUILDARGS is not).

If you depend on Catalyst 5.8, then all Moose features work as expected.

If you have any code which installs anonymous subroutine references directly into the symbol table, you may encounter breakages. The simplest solution is to use Sub::Name to name the subroutine. Example:

With Catalyst 5.80 this won't work anymore, because Catalyst no longer uses NEXT.pm for method resolution. The functionality was only ever originally operational as NEXT remembers what methods have already been called, and will not call them again.

Using this now causes infinite recursion between MyApp::setup and Catalyst::setup, due to other backwards compatibility issues related to how plugin setup works. Moose method modifiers like before|after|around setup => sub { ... }; also will not operate correctly on the setup method.

The right way to do it is this:

after setup_finalize => sub {
... # things to do after the actual setup
};

Previously, if you had a component which inherited from Catalyst::COMPONENT, but overrode the new method to return false, then your class's configuration would be blessed into a hash on your behalf, and this would be returned from the COMPONENT method.

This behavior makes no sense, and so has been removed. Implementing your own new method in components is highly discouraged. Instead, you should inherit the new method from Catalyst::Component, and use Moose's BUILD functionality and/or Moose attributes to perform any construction work necessary for your class.

Previously, Catalyst's COMPONENT method would delegate to the method on the right hand side, which could then delegate back again with NEXT. This is poor practice, and in addition, makes no sense with C3 method dispatch order, and is therefore no longer supported.

If a COMPONENT method is detected in the inheritance hierarchy to the right hand side of Catalyst::Component::COMPONENT, then the following warning message will be emitted:

There is a COMPONENT method resolving after Catalyst::Component
in ${next_package}.

The correct fix is to re-arrange your class's inheritance hierarchy so that the COMPONENT method you would like to inherit is the first (left-hand most) COMPONENT method in your @ISA.

Previously, the development server would allow propagation of system environment variables into the request environment, this has changed with the adoption of Plack. You can use Plack::Middleware::ForceEnv to achieve the same effect.

Having actions in your application class will now emit a warning at application startup as this is deprecated. It is highly recommended that these actions are moved into a MyApp::Controller::Root (as demonstrated by the scaffold application generated by catalyst.pl).

This warning, also affects tests. You should move actions in your test, creating a myTest::Controller::Root, like the following example:

The first time one of these methods is called, a warning will be emitted:

Class $class is calling the deprecated method Catalyst::Dispatcher::$public_method_name,
this will be removed in Catalyst 5.9

You should NEVER be calling any of these methods from application code.

Plugin authors and maintainers whose plugins currently call these methods should change to using the public API, or, if you do not feel the public API adequately supports your use case, please email the development list to discuss what API features you need so that you can be appropriately supported.

In this version of Catalyst, if a component is loaded from disk, but no symbols are defined in that component's name space after it is loaded, this warning will be issued:

require $class was successful but the package is not defined.

This is to protect against confusing bugs caused by mistyping package names, and will become a fatal error in a future version.

Please note that 'inner packages' (via Devel::InnerPackage) are still fully supported; this warning is only issued when component file naming does not map to any of the packages defined within that component.